Methods for producing 1,3-butadiene as many petrochemical product intermediates include naphtha cracking, direct dehydrogenation of normal-butene, and oxidative dehydrogenation of normal-butene. Among such methods, naphtha cracking process entails substantial energy consumption due to a high reaction temperature and requires establishment or expansion of new naphtha crackers to meet an increasing demand for 1,3-butadiene through naphtha cracking. However, this process is not preferred since it is not an exclusive process for production of only 1,3-butadiene, does not optimally match investment and operating for naphtha crackers to production and demand of 1,3-butadiene, and disadvantageously causes production of other feedstock, in addition to 1,3-butadiene.
Accordingly, there is a need for a method for exclusively producing 1,3-butadiene. As an alternative method to naphtha cracking, a method for producing 1,3-butadiene from normal-butene by dehydrogenation has been suggested.
Dehydrogenation of normal-butene includes direct dehydrogenation and oxidative dehydrogenation, which direct dehydrogenation of normal-butene is an endothermic reaction having considerably high reaction heat, is required for high-temperature and low-pressure conditions to produce 1,3-butadiene at a high yield as thermodynamically unfavorable and is not suitable for a commercial process to produce 1,3-butadiene.
On the other hand, oxidative dehydrogenation of the normal-butene is a reaction in which normal-butene reacts with oxygen to produce 1,3-butadiene and water, and is thermodynamically very favorable since stable water is obtained as a kind of products. In addition, oxidative dehydrogenation is exothermic, unlike the direct dehydrogenation of normal-butene, can be obtained in a high-yield 1,3-butadiene at a low reaction temperature, as compared to the direct dehydrogenation and is very suitable for commercialization process as Do not require additional heat supply.
Hence, in spite of the Oxidative dehydrogenation effectively from normal-butene (1-butene, trans-2-butene or cis-2-butene) to 1,3-butadiene alone, it is expected many side reactions such as complete oxidation, since it uses oxygen as a reactant. The reaction mechanism of oxidative dehydrogenation of normal-butene is not yet precisely known, but it is known as C—H bond-cleavage from normal-butene at the same time oxidation-reduction reactions of the catalyst itself and accordingly, catalysts of metal composite oxide type having various oxidation states may be used for the oxidative dehydrogenation.
Accordingly, all the above catalysts are catalysts having a specific crystal structure. Of these, bismuth molybdate-based catalysts and ferrite-based catalysts have been reported to exhibit high activity in oxidative dehydrogenation of normal-butene.
Of these, the bismuth molybdate-based catalysts are pure bismuth molybdate catalyst consisting of solely bismuth and molybdenum oxide and multi-component bismuth molybdate catalyst-added various metals.
It is known that three phases of α-bismuth molybdate (Bi2Mo3O12), β-bismuth molybdate (Bi2Mo2O9) and γ-bismuth molybdate (Bi2MoO6) of the pure bismuth molybdate catalyst can be used as catalysts. However, 1,3-butadiene manufacturing process by normal-butene oxidative dehydrogenation is unsuitable for commercialization processes due to limit on increase in yield of 1,3-butadiene yield.
Several patents and literatures has ever been reported for multi-component bithmuth molybdate-based catalysts for the oxidative dehydrogenation of normal-butene. Specifically, it is reported to be obtained 1,3-butadiene at a yield of up to 62% by performing oxidative dehydrogenation of a C4 mixture containing normal-butane and normal-butene at 470° C. using complex oxides catalysts consisting of cobalt, iron, bismuth, magnesium, potassium and molybdenum (U.S. Pat. No. 3,998,867), and it is reported to be obtained 1,3-butadiene at a yield of up to 63% by performing oxidative dehydrogenation of 1-butene at 320° C. using complex oxides catalysts consisting of nickel, cobalt, iron, bismuth, phosphorus, potassium and molybdenum (U.S. Pat. No. 3,764,632).
Multi-component bismuth molybdate catalysts stated in the literatures enable production of 1,3-butadiene at a high yield through the oxidative dehydrogenation of 1-butene, but exhibit low activity to 2-butene. On the other hand, ferrite-based catalysts exhibit production of 1,3-butadiene at a high yield through oxidative dehydrogenation of 2-butene, but exhibit low activity to 1-butene.
In order to resolve differences between the reactivity of butene isomers, Korean Patent Publication No. 2009-0103424 suggests bilayer of a multi-component bismuth molybdate catalyst and a ferrite catalyst charged in a reactor, but this method can be affected on yields depending on the composition of the reactants and two kinds of catalysts with different characteristics need to react under the same reaction conditions.
Accordingly, the present inventors were developed catalysts exhibiting different activities depending on isomers using a multi-component bismuth molybdate catalyst and were attempt to maximize the yield of 1,3-butadiene by each charged into the reactor connected in parallel.